When you say trial and error, are you referring to the method by which you adjust the pivot point until 2 vertical edges (eg dor frames) one close and one farther out cease to move relative to one another? That had been the recommendation I've most often seen rather than trying to get stats - also with sme zooms, it will vary depending on the fl.

Tim,The only way as far as I'm concerned is to do it the way you've described, especially if you're using a zoom lens.

Manfrotto have some intructions available by going to www.bogenimaging.us/ Once at the website, select Manfrotto, then select "Heads...QTVR" then select any one of the QTVR heads "303" for example then once in, scroll down to the line "Click here to learn more about the exciting advantages of Pano / VR photography from Manfrotto's new site" (it is just above the specifications)jules